Heretofore, elastomeric torsion springs or rubber torsion springs have been made by concentrically positioning cylindrical sleeves of metal of different diameters and securing a resilient material, such as an elastomer, therebetween. The inner sleeve is secured to a first element which is to be resiliently carried for torsional movement and the outer cylindrical sleeve is secured to another or second element such as a housing and with respect to which the first element has relative torsional movement.
FIG. 1 illustrates a prior elastomeric torsion spring 10 which includes an elastomeric member 12 disposed between and bonded to an inner sleeve 14 and an outer shell 16. Typically, outer shell 16 is anchored and inner sleeve 14 is keyed so that a shaft 18 extending therethrough can be utilized to rotate the inner sleeve 14 with respect to the outer shell 16. Under these circumstances, shaft 18 and outer shell 16 must be connected to parts of a device which are intended to move relative to one another.
FIG. 2 illustrates an elastomeric spring having an outer shell 26 which rotates in a direction opposite to an inner sleeve 22. A center shaft 20 of the inner sleeve 22 is keyed, thereby allowing the shaft 20 to be rotated by a keyed rod (not shown) with respect to the outer shell 26. The outer shell 26 therefore must be connected or anchored to something which has torsional movement with respect to the inner shaft. Each spring arranged and utilized in such a manner has a particular windup or spring rate curve to describe the amount of torque provided by the spring for any given angular displacement or torsional movement between the inner sleeve and the outer shell.
FIG. 3 illustrates a torque versus windup curve of a typical prior elastomeric spring such as is shown in FIG. 1. Designers who incorporate an elastomeric spring such as illustrated in FIG. 1 utilize the torque versus windup characteristics to anticipate the amount of torque produced by the spring at any particular given amount of angular displacement.
Sometimes, however, it is necessary to have a spring which can provide varying torque for a particular windup. Heretofore, it has been necessary to change springs to achieve varying torque. It is not always practical however to change springs in a structure in order to achieve this objective.
An elastomeric spring which can provide varying torque vs. windup is, therefore highly desirable.